1. Field of the Invention
This invention relates to signal transmission systems in digital controller systems, and more particularly to a signal transmission system in such a digital controller system in which the signal transmission efficiency is improved.
2. Discussion of the Prior Art
A conventional instrumentation system comprises analog instruments and controlling computers. Recently, a digital control system utilizing a microcomputer as its indicating controller has been put in practical use. In the digital control system, a variety of accurate functions, which cannot be provided by a conventional analog indicating controller, are provided for the instrumentation system (cf. U.S. Pat. No. 4,118,772).
In the control system, a hierarchy system is established. More specifically, the system comprises a high level control section, a plurality of low level control sections which are monitored and controlled by the high level control section, and a plurality of loop station means connected to each of the low level control sections. In the signal transmission between these elements, the high level control section has precedence over the others. In order to minimize transmission errors, a return and collation system is employed for the signal transmission. For instance, in the data transmission between the low level control section and the loop station means, first a relevant instruction is transmitted from the low level control section to the loop station means. Upon receiption of the instruction, the loop station means returns the instruction, as it is, to the low level control section. The low level control section subjects the instruction thus returned to collation to determine if it is identical to the initial one, and then transmits the instruction to the loop station means again. Alternatively, the loop station means collates the instruction transmitted thereto with the instruction transmitted initially thereto to determine if these two instruction are equal in content, and receives the instruction only when the two instructions are determined identical. The same operation as described above is carried out in the case of data transmission between the high level control section and the low level control section.
However, the system suffers from a difficulty that, since the return and collation system is employed for data transmission, the data transmission efficiency is low.
Furthermore, in the case of an integrated direct digital control (DDC) system combined with a cathode ray tube display unit, the quantity of data to be processed is considerably increased. Therefore, the conventional signal transmission system is disadvantageous in that the processing rate is necessarily low.